1. Field of Invention
The present invention relates generally to the fabrication of integrated circuits chips. More particularly, the present invention relates to a nesting apparatus that is suitable for supporting a substrate during a dicing process.
2. Background
During the fabrication of integrated circuit chips, multiple integrated circuit chips are often arranged on a single substrate, e.g., wafer or circuit board, which is eventually diced to separate the integrated circuit chips. Although a substrate may be sawed, or diced, to create individual chips at substantially any point during an overall fabrication process, the substrate is typically sawed after ball grid arrays and dies are formed on the substrate.
FIG. 1a is a diagrammatic representation of a contact, or ball grid array (BGA) side of a conventional substrate. A substrate 102 includes individual integrated circuit chips 112, each of which includes a ball grid array 110 of contacts, as will be appreciated by those skilled in the art. In general, the number of integrated circuit chips 112 formed on substrate 102 may vary, depending upon the size of substrate 102 and the size of each integrated circuit chip 112. Further, the number of balls in each ball grid array 110 may also vary. By way of example, as shown, substrate 102 includes one hundred and forty integrated circuit chips 112, each of which have a ball grid array with sixteen balls.
Substrate 102 also generally includes locator holes 106 which are used for various fabrication processes including, but not limited to, processes used to apply ball grid arrays 110 on chips 112 and processes used to encapsulate substrate 102. xe2x80x9cPick-up pointsxe2x80x9d 116, which are also included on substrate 102, are arranged to enable cameras to check the overall alignment of substrate 102, as necessary, during fabrication.
A representation of the non-BGA side of substrate 102 is shown in FIG. 1b. Non-BGA side of substrate 102 may be considered to be the xe2x80x9cdie-sidexe2x80x9d of substrate 102, as non-BGA side typically includes integrated circuit dies 140. As will be appreciated by those skilled in the art, when substrate 102 is diced to form individual integrated circuit chips 112, one side of each integrated circuit chip 112 will have ball grid array 110, while the other side will have integrated circuit dies 140.
As mentioned above, in order to separate integrated circuit chips from a substrate, the substrate must be diced with a dicing saw or similar device. Typically, a dicing process involves manually placing the substrate, non-BGA side down, on an adhesive surface, e.g., tape. The tape is arranged to hold the individual integrated circuit chips in place, both during and after dicing. Specifically, the tape is used to prevent the individual integrated circuit chips from rotation and translation with respect to one another.
A substrate is cut from the BGA side, i.e., a substrate is cut with the non-BGA side down, since it is difficult for tape to effectively grip and hold the balls in ball grid arrays, either from the bottom surfaces of the balls or from the side surfaces of the balls. In other words, while tape is capable of securely holding a substantially smooth surface such as the dies on a substrate during dicing, the tape is not as effective in securely holding an uneven surface, such as the overall surface of ball grid arrays, during dicing.
Once a substrate is placed on tape with the BGA side up, the tape and the substrate are manually loaded on a vacuum chuck for dicing. In other words, the tape and the substrate are aligned on a vacuum chuck, tape-side down, such that the vacuum from the vacuum chuck effectively xe2x80x9cgripsxe2x80x9d the tape and the board. While the tape and the substrate are held on the vacuum chuck, a dicing saw is used to automatically dice the integrated circuit chips. As will be appreciated by those skilled in the art, the dicing saw dices the substrate to form the integrated circuit chips, substantially without cutting through the tape.
Once the integrated circuit chips are separated, the chips must be removed from the tape. A vacuum is generally not used to remove the chips from the tape, since the chips are often not accurately aligned on the tape. Typically, a person may remove each chip, BGA side up, from the tape, then place each chip, BGA side down, in a holding tray which may be used to transport the chips to a subsequent fabrication process. The use of manual processes, however, is often time-consuming and inaccurate.
Alternatively, in lieu of a manual process, a pick-and-place machine may be used to remove the chips from the tape, and place the chips in holding trays. As was the case with manually removing chips from the tape, the use of pick-and-place machines is often time consuming. By way of example, a pick-and-place machine must line up each chip prior to picking that chip off the tape. In addition, pick-and-place machines are additional pieces of fabrication equipment that are generally separate from dicing machines. Therefore, an overall dicing process is likely to require an additional manual process of transporting the tape and the diced chips to the pick-and-place machine.
The use of tape in dicing processes is often undesirable as the tape may be relatively expensive, and must be disposed of once the dicing process is completed. In addition, adhesives on the tape may remain on a chip after the dicing process, thereby creating residue that may be difficult to remove. When residue is not properly removed from a chip, subsequent fabrication steps, as well as the integrity of the chip, may be compromised. The use of tape also generally requires manual handling, e.g., placing a substrate on tape. As will be appreciated by those skilled in the art, in addition to being both tedious and time consuming, manual processes often increase the likelihood that a substrate may be mishandled or become contaminated.
Hence, what is desired is a method and an apparatus for efficiently and substantially automatically dicing a substrate to form individual integrated circuit chips. In other words, what is desired is a method and an apparatus for securely holding a substrate, without the use of tape, during a dicing process.
The present invention relates to a nest mechanism which is arranged to support a substrate during a dicing process, and methods for using such a nest mechanism. According to one aspect of the present invention, a nest apparatus supports a substrate, which includes a chip, a first side, and a second side, during a dicing process, includes an alignment mechanism that positions the substrate with respect to the nest apparatus. The nest apparatus also includes a grid arrangement that defines an opening which receives a contact which is included on the second side of the substrate. In one embodiment, the alignment mechanism is an alignment pin that engages the substrate, as for example through an opening in the substrate, to hold the substrate.
In another embodiment, the second side of the substrate includes a ball grid array, wherein the contact is a part of the ball grid array, and the opening accommodates the ball grid array. In still another embodiment, the nest apparatus also includes a holding mechanism which secures the nest apparatus to a dicing apparatus that is used to cut the substrate. In such an embodiment, the holding apparatus may specifically be arranged to effectively secure the nest apparatus to a vacuum chuck associated with the dicing apparatus.
According to another aspect of the present invention, a method for cutting a substrate without using tape to hold the substrate includes retaining the substrate within a nest mechanism that holds the substrate during cutting with a second side of the substrate facing down, or into the nest mechanism. The method also includes positioning the nest mechanism on a vacuum chuck associated with a cutting mechanism that also includes a vacuum chuck and a cutting saw, and engaging the second side of the substrate through the nest mechanism against the vacuum chuck with a vacuum generated by the vacuum chuck. Finally, the substrate is cut from the first side, using the cutting saw. In one embodiment, engaging the second side against the vacuum chuck with the vacuum involves retaining a side surface of a ball in a ball grid array, which is located on the second side of the substrate, against the nest mechanism, and engaging the ball grid array with the vacuum through the nest mechanism.
In another embodiment, cutting the substrate from the first side involves separating a chip, which is defined within the substrate, from the substrate. In such an embodiment, cutting the substrate may also include constraining the separated chip from translational movement by retaining the side surface of the ball against the nest mechanism and engaging the ball grid array with the vacuum from the vacuum chuck.
In accordance with yet another aspect of the present invention, a method for cutting a substrate which has a substantially smooth side and a substantially unsmooth side includes retaining the substrate within a nest mechanism, wherein retaining the substrate includes aligning the substrate within the nest mechanism such that the substrate is substantially constrained from translational and rotational movement. The method further includes positioning the nest mechanism on a vacuum chuck, engaging the substrate through the nest mechanism against the vacuum chuck, and cutting the substrate with a cutting mechanism. In one embodiment, retaining the substrate within the nest mechanism also includes placing the substrate in the nest mechanism with the substantially unsmooth, e.g., the ball grid array side, side facing down. In another embodiment, the substrate is cut from the substantially smooth side, e.g., the die side.
In accordance with another aspect of the present invention, a nest apparatus having a first surface and a second surface supports a substrate with a first side and a second side in conjunction with a vacuum retainer plate during a dicing process. The substrate is placed, BGA side up, into the nest apparatus which is then mounted onto the vacuum retainer plate arrangement for dicing. In another embodiment, the substrate is lifted off the first surface of the nest when the nest is mated with the vacuum retainer plate.